1. Field of the Invention
The present invention relates to a development device and method used in a copier, a facsimile machine, a printer, and so forth, and more particularly to a development device and method using a two component developer including toner and a magnetic carrier, capable of maintaining a toner concentration at a constant level without shortening the life of the developer, and a process cartridge and image forming apparatus using the development device.
2. Discussion of the Background
A background development device using a two component developer including toner and a magnetic carrier has a configuration shown in FIG. 1. As shown in FIG. 1, a development device 4a includes a development roller 5a serving as a developer bearing member, an agitation and conveyance path 10a, an agitation and conveyance auger 11a serving as an agitation and conveyance member, a supply and collection auger 401, a supply and collection path 402, and a partition 403 serving as a partition member.
The agitation and conveyance path 10a includes the agitation and conveyance auger 11a, while the supply and collection path 402 includes the supply and collection auger 401. As shown in FIG. 1, the supply and collection auger 401 and the agitation and conveyance auger 11a are arranged side by side in a horizontal direction. The agitation and conveyance path 10a and the supply and collection path 402 are partitioned by the partition 403. The partition 403 includes an opening at each end in a longitudinal direction thereof, connecting the agitation and conveyance path 10a and the supply and collection path 402.
The supply and collection auger 401 supplies developer to the development roller 5a. The development roller 5a supplies the developer to a latent image bearing member (not shown). The supply and collection auger 401 then collects developer having been used for development from the development roller 5a. The collected developer is conveyed to a downstream end in a conveyance direction of the supply and collection auger 401, and is transferred into the agitation and conveyance path 10. 
The agitation and conveyance auger 11a is provided with the collected developer, and toner as necessary. While agitating the developer and the toner, the agitation and conveyance auger 11a conveys the developer mixed with the toner in a direction opposite to the conveyance direction of the supply and collection auger 401.
The developer is circulated in the agitation and conveyance path 10a and the supply and collection path 402 through the openings of the partition 403.
When the developer is used for development, a toner concentration of the developer decreases as the toner is consumed for development. Therefore, the collected developer has a toner concentration lower than a toner concentration of the developer yet to be used for development.
In the development device 4a, as the developer is supplied and collected by the same auger by using the same path, the collected developer is mixed with the developer yet to be used for development during agitation. As a result, the toner concentration of the developer to be supplied to the development roller 5a is lower as the developer is conveyed further downstream in the supply and collection path 402. Especially when an image with high coverage is developed, the development consumes a large amount of toner and significantly lowers the toner concentration of the developer at a downstream side in the conveyance direction, resulting in a problem such that image quality may hardly be maintained.
Increasing an amount of developer to be conveyed can solve the problem. However, an increase in the amount of developer imposes increased stress on the developer, causing a shortening of life of the developer.
The above problem can be solved by separately providing an auger for supplying developer to a development roller and an auger for collecting developer having been used for development in different conveyance paths.
Configurations of development devices 4b, 4c, and 4d each provided with the different conveyance paths are described below referring to FIGS. 2, 3, and 4, respectively.
As shown in FIG. 2, the development device 4b includes a development roller 5b, a supply and conveyance auger 8b, a supply and conveyance path 9b, a collection and agitation auger 110, an accumulation prevention auger 209, a collection and agitation path 210, and a partition 403b serving as a partition member.
The supply and conveyance path 9b includes the supply and conveyance auger 8b, while the collection and agitation path 210 includes the collection and agitation auger 110. The supply and conveyance auger 8b is arranged above the collection and agitation auger 110. The supply and conveyance path 9b and the collection and agitation path 210 are partitioned by the partition 403b. The partition 403b includes an opening at each end in a longitudinal direction thereof, connecting the supply and conveyance path 9b and the collection and agitation path 210.
The supply and conveyance auger 8b supplies developer to the development roller 5b while conveying the developer. The developer passes by a development area on the development roller 5b, and is collected into the collection and agitation path 210. Surplus developer conveyed to a downstream end in the supply and conveyance path 9b without being used for development falls through one of the openings located at the downstream end therein into the collection and agitation path 210.
The collection and agitation auger 110 agitates and conveys the collected and surplus developer in a direction opposite to a conveyance direction of the supply and conveyance auger 8b. The conveyed developer is jammed into a downstream end in the collection and agitation path 210, and rises therein by conveyance force of the collection and agitation auger 110. As a result, the developer is supplied through the other opening located in the downstream end therein into the supply and conveyance path 9b. 
The collection and agitation path 210 is provided with the accumulation prevention auger 209 for preventing excessive developer from accumulating at the downstream end therein, and for conveying the excessive developer in an upstream direction.
In the development device 4b, the developer having been used for development is collected into the collection and agitation path 210, and is not mixed into the supply and conveyance path 9b. Therefore, the developer in the supply and conveyance path 9b maintains a toner concentration at a constant level, and as a result, the development roller 5b is supplied with the developer having a constant toner concentration.
As shown in FIG. 3, the development device 4c includes a development roller 5c, a collection and conveyance auger 6c, a collection and conveyance path 7c, a supply and conveyance auger 8c, a supply and conveyance path 9c, an agitation and conveyance path 10c, an agitation and conveyance auger 11c, first and second partitions 404 and 405 serving as partition members.
The supply and conveyance path 9c includes the supply and conveyance auger 8c, while the agitation and conveyance path 10c includes the agitation and conveyance auger 11c. The supply and conveyance auger 8c is arranged above the agitation and conveyance auger 11c. The supply and conveyance path 9c and the agitation and conveyance path 10c are partitioned by the first partition 404. The first partition 404 includes an opening at each end in a longitudinal direction thereof, connecting the supply and conveyance path 9c and the agitation and conveyance path 10c. 
The collection and conveyance path 7c includes the collection and conveyance auger 6c. The collection and conveyance path 7c and the agitation and conveyance path 10c are arranged side by side in a horizontal direction, and are partitioned by the second partition 405. The second partition 405 includes an opening at a downstream end in a conveyance direction of the collection and conveyance auger 6c, connecting the collection and conveyance path 7c and the agitation and conveyance path 10c. 
The supply and conveyance auger 6c supplies developer to the development roller 5c while conveying the developer in the same conveyance direction as the collection and conveyance auger 6c. The developer passes by a development area on the development roller 5c, and is collected into the collection and conveyance path 7c. The collection and conveyance auger 6c conveys the collected developer to the downstream end in the conveyance direction thereof. The collected developer is transversely transferred into the agitation and conveyance path 10c through the opening of the second partition 405.
Surplus developer conveyed to a downstream end in the supply and conveyance path 9c without being used for development falls through one of the openings located at the downstream end therein into the agitation and conveyance path 10c. 
The agitation and conveyance auger 11c agitates and conveys the surplus and collected developer in a direction opposite to the conveyance direction of the supply and conveyance auger 8c. The conveyed developer is jammed into a downstream end in the agitation and conveyance path 10c, and rises therein by conveyance force of the agitation and conveyance auger 11c. As a result, the developer is supplied through the other opening located in the downstream end therein into the supply and conveyance path 9c. 
In the development device 4c, the developer having been used for development is collected into the collection and conveyance path 7c, and is not mixed into the supply and conveyance path 9c. Therefore, the developer in the supply and conveyance path 9c maintains a toner concentration at a constant level, and as a result, the development roller 5c is supplied with the developer having a constant toner concentration.
As shown in FIG. 4, the development device 4d includes a development roller 5d, a collection and conveyance auger 6d, a collection and conveyance path 7d, a supply auger 440, a conveyance auger 450, a supply and conveyance path 9d, an agitation and conveyance path 10d, an agitation and conveyance auger 11d, first and second partitions 404d and 405d serving as partition members.
The collection and conveyance path 7d includes the collection and conveyance auger 6d arranged above the conveyance auger 450. The supply and conveyance path 9d includes the supply and conveyance augers 440 and 450 arranged next to each other. The agitation and conveyance path 10d includes the agitation and conveyance auger 11d. The supply and conveyance augers 440 and 450, and the agitation and conveyance auger 11d are arranged in a substantially horizontal direction.
The supply and conveyance path 9d and the agitation and conveyance path 10d are arranged side by side, and partitioned by the first partition 404d. The first partition 404d includes an opening at each end in a longitudinal direction thereof, connecting the supply and conveyance path 9d and the agitation and conveyance path 10d. 
The collection and conveyance path 7d arranged above the supply and conveyance path 9d, and the supply and conveyance path 9d are partitioned by the second partition 405d. The second partition 405d includes an opening at a downstream end in a conveyance direction of the collection and conveyance auger 6d, connecting the collection and conveyance path 7d and the supply and conveyance path 9d. 
The supply auger 440 supplies developer to the development roller 5d while conveying the developer. The conveyance auger 450 conveys the developer in the same conveyance direction as the supply auger 440. The developer is collected from the development roller 5d at a higher position than a position in which the supply auger 440 faces the development roller 5d. The collection and conveyance auger 6d conveys the collected developer to the downstream end in the same conveyance direction as the supply and conveyance augers 440 and 450. The collected developer falls through the opening of the second partition 405d into the supply and conveyance path 9d. 
Surplus developer conveyed to a downstream end in the supply and conveyance path 9d by the supply and conveyance augers 440 and 450 without being used for development is, together with the collected developer, transversely transferred through one of the openings of the first partition 404d located at the downstream end therein into the agitation and conveyance path 10d. 
The agitation and conveyance auger 11d conveys the surplus and collected developer to a downstream end in a direction opposite to the conveyance direction of the supply and conveyance augers 440 and 450. The surplus and collected developer is transversely transferred through the other opening of the first partition 404d located at the downstream end therein into an upstream side of the supply and conveyance path 9d. 
In the development device 4d, the developer having been used for development is collected into the collection and conveyance path 7d, and is less likely to be mixed into the supply and conveyance path 9d. Therefore, compared with the development device 4a, the developer to be supplied to the development roller 5d has smaller fluctuations in toner concentration. Further, as the developer is substantially horizontally circulated in the development device 4d, shortening of life of developer attributed to forced upward transferring of developer can be prevented.